No, have never heard of them or looked into this.
Why do you want this? You have the option of forwarding your landline to your mobile whenever you are out of the office.
What I did was to set up a 'virtual business line' with a VOIP service provider and I can change the destination number any time I want depending on where I am, so that if anybody calls my advertised company number it routes to that phone. It simultaneously forwards to my mobile, so if I'm in the office or out and about, I'll always get the call.
However my business is not customer facing, as I deal with a limited number of large organisations, so maybe such a solution would not suit you